1. Field of the Invention
The present invention relates generally to printed circuit board (PCB) manufacturing and processing technique, and more particularly to a clamping mechanism automatically adaptable to change of thickness of printed circuit board.
2. Description of the Related Art
A printed circuit board has a substrate made of such as glass epoxy material. Predetermined circuits are formed on the substrate by means of the conventional transfer printing and etching techniques. Then proper electronic components are electrically connected to the printed circuit board to serve as a part of an electronic equipment. All kinds of electronic equipments have become more and more complicated over the years. As a result, multilayer PCB substrate made of up to 100 layers by lamination has been developed instead of the traditional single-layer substrate. No matter how many layers the PCB substrate has, in the manufacturing process of the PCB, the PCB must be tested by means of optical scanning or flying probe tester to ensure that the PCB is free from short-circuit or breakage and thus ensure good quality of the product.
In the automated manufacturing process of the printed circuit board, a conveyor 1 is used to horizontally move the printed circuit board as shown in FIG. 1. The conveyor 1 has two parallel clamping rail members 2 for clamping two sides of the printed circuit board. The conveyor 1 further has a transmission mechanism 3 for linearly moving the printed circuit board, which is held between the clamping rail members 2. Under such circumstance, the printed circuit board can be stably horizontally moved in the manufacturing or processing process for, such as the test.
However, as aforesaid, the thickness of the printed circuit board varies. Therefore, in the conventional conveyor 1, the gap between two clamping rails of the clamping rail member 2 is adjustable in accordance with the thickness of the printed circuit board. To speak more specifically, the gap between the clamping rails is directly changed by a conventional reciprocating drive device 4 such as a pneumatic cylinder or an electromagnetic cylinder according to the thickness of the printed circuit board. Such drive device 4 is not a multipoint control unit so that the gap between the clamping rails can be simply changed in one single state. Accordingly, in the case of too small gap, the printed circuit board with a different thickness may be damaged due to excessively great clamping force. On the other hand, in the case of too large gap, the printed circuit board may loosen due to insufficient clamping force. Therefore, the conventional linear drive device can be hardly reliably used to adjust the gap between the clamping rails.